docs: api comments say what the endpoints do, not how they came to be (#6277)

Rewrites the internal/api comment blocks to rule 32: task, milestone and
rule ids gone, the stories behind them restated as the constraint they
left, stale references corrected (the stream secret is wired from config,
the timezone handler already refreshes the scheduler, the Android app is
the native client, the design docs cited are not in the repo). Also
rewraps comment lines over 80 columns left by the earlier batches.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/library.go

@@ -119,7 +119,8 @@ func (h *handlers) handleGetArtist(w http.ResponseWriter, r *http.Request) {
 	}
 	refs := make([]AlbumRef, 0, len(rows))
 	for _, row := range rows {
-		// durationSec=0: not aggregated for nested album lists per spec data flow.
+		// durationSec=0: not aggregated for nested album lists per spec data
+		// flow.
 		refs = append(refs, albumRefFrom(row.Album, artist.Name, int(row.TrackCount), 0))
 	}
 	genres, err := q.ListGenresForArtist(r.Context(), artist.ID)
@@ -257,7 +258,7 @@ func (h *handlers) handleGetArtistTopTracks(w http.ResponseWriter, r *http.Reque
 
 // handleLibraryShuffle implements GET /api/library/shuffle?limit=N —
 // the online source for the client's always-present "Shuffle all"
-// (#427 S4). N random tracks across the whole library, per-user
+// N random tracks across the whole library, per-user
 // quarantine filtered. limit defaults to 100, clamped to 1..500.
 // Offline, the client shuffles its local cache instead and never
 // calls this.